Freehand and eraser tool

The freehand tool is the basic drawing tool.

You can adjust the settings of the selected brush in the tool dock.
A brush can work in three different modes: hard-edged pen (useful for pixel art), soft edged brush (normal mode) and watercolor mode. In watercolor mode, the brush picks up color from the canvas as you paint.

Other settings you can change are the brush blending mode and whether it works in direct or indirect mode.

Every brush also has an eraser mode. This can be toggled by clicking on the little eraser button.

There are five tool slots for storing different brush settings and one extra slot dedicated for a brush in
eraser mode. When using the eraser tool, only the eraser slot is available.

See also the input dock. From there you can adjust the strength of the pen motion smoother as well
as the pen pressure response curve.

There is also a brush preset dock that lets you save and restore brush presets. Unlike the brush slots (1-5),
changes to the selected brush does not automatically change the preset.

Straight line, Rectangle and Ellipse

These brush tools let you draw geometric shapes. Certain extra buttons are available for use with these:

When holding down shift, the line is constrained to an angle that is multiple of 45°. With
the rectangle tool, the shape is constrained to a square and with the ellipse tool a circle.

When holding down alt, the starting point of the shape becomes the center point.

Bezier curve

This tool lets you draw bezier curves. Click and drag to add a curve segment and
adjust the new segments control points. Right click (or undo) to cancel a segment.
Adding a straight segment ends the curve. The curve can also be ended by hitting Return,
in which case the unfinished segment is not added.

Flood fill

This is a tool for filling closed areas.
The tolerance slider adjusts the color matching tolerance.
The expand slider controls how much the fill will expand outside the original borders.
It is useful for filling in areas bounded by smooth strokes.
You can also set a size limit: the fill will be cancelled if it would fill more than this area.
The size limit helps prevent accidental layer fills in online mode that would annoy other users.

When fill under is checked, the color fill is blended as if it were on a layer below.
It is only used when filling a transparent area.
The picture on the left was filled with fill-under enabled, and the right one without it:

Annotation

Annotations are floating text layers.
Annotation content, font and color can be edited in the tool dock.

Checking the protect box will prevent other users from modifying an annotation you have created.
Session operators can also limit the creation of new annotations.

Clicking on the merge button will convert the annotation to an image and merge it with the current layer.
Note that due to differences in fonts and operating systems, unmerged annotations may look entirely different to different users!

Color picker

The color picker is used to pick colors from the image.
Its an easy way to build palettes by sampling colors from a picture, then dragging them onto a new palette.

You can also pick colors quickly when using any tool by holding down the Control key.

Laser pointer

This is a virtual laser pointer for pointing at things on the canvas.
When track hovering pointer is checked, the pointer location is updated even when the mouse button/stylus is not pressed.
Painting with the laser pointer draws an animated laser trail that fades away after a while.
Laser trails and user pointers can be disabled from the View menu.

Selection

There are two selection tools: rectangular and freeform (lasso).
These allow you to select regions for copy & pasting and transformation.

The selected region can be resized and rotated.
Drag the handles to resize or hold Alt and drag to rotate.

Hitting Del will delete the selected layer content without dismissing the selection.